Wind power installations generally comprise one or more wind turbines connected to a grid or other such network. Typical installations comprise several wind turbines and are generally known as ‘wind farms’. The wind turbines each comprise a rotor, which is mounted to a nacelle located at the top of a tower. The rotor has a plurality of blades, and is connected via a rotor shaft to a generator located inside the nacelle. The output of the generator is connected to a converter, which generally comprises a rectifier for converting the AC voltage output of the generator into a DC voltage, and an inverter for converting the DC voltage to an AC voltage having a frequency compatible with the grid frequency. The output from the converter is connected to a main transformer (also referred to as a high-voltage (HV) transformer) of the wind turbine, which converts the relatively low-voltage output from the generator into a high voltage suitable for transmission to the grid or to an intermediate substation supplying a power or utility grid.
Most modern wind turbines also include an auxiliary transformer (also referred to as a low-voltage (LV) transformer) that provides a source of low-voltage (typically about 120-400 V) AC power to the nacelle. This auxiliary transformer supplies a number of auxiliary components within the nacelle, such as lighting, which is required when maintenance personnel are working within the nacelle. The auxiliary transformer also provides a source of power to the pitch and yaw mechanisms, which allows these systems to be operated even when the turbine is not generating power. The auxiliary transformer is generally housed within the nacelle and is connected on the low-voltage side of the main transformer, taking its input from the converter output. An auxiliary transformer may also be associated with a substation, in which case the auxiliary transformer may supply a plurality of wind turbines.